Feedback/registration mechanism for ultrasound devices

ABSTRACT

Among other things, there is disclosed structure and methods for registering images obtained through internal (e.g. intravascular) ultrasound devices. Embodiments of a device with a rotating ultrasound beam is provided, with a wall of the device being anisotropic in ultrasound passage. As examples, a cable opaque to ultrasound is attached along the wall of the device, so that the ultrasound beam at the location of the cable is blocked, reflected or scattered. As another example, a thin film of metallic material is placed on or in the wall to allow a portion of the beam to be blocked or attenuated. The imaging system recognizes the changes to the signals made by the anisotropic wall, and registers successive images according to those changes.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. ProvisionalApplication Ser. No. 61/713,142, filed on Oct. 12, 2012, andincorporates by reference the same herein in its entirety.

The present disclosure concerns ultrasound devices for use internallyand resolution of problems existing in rotating mechanical scanultrasound devices.

BACKGROUND

A number of ultrasound imaging devices and systems have been proposed,and in many the problem exists of ensuring that each of the frames of animage acquired by the ultrasound device are properly registered witheach other. Without such registration, there is the possibility thatvariance in mechanical movement of an ultrasound transducer, orinadvertent or purposeful movement of the device, will be unaccountedfor in the image observed by the physician, resulting in undesirablechanges in orientation or content of images.

For example, there are proposed devices in which an ultrasoundtransducer is turned (e.g. by a motor) around a longitudinal axis of thedevice (e.g. U.S. Pat. No. 8,214,010 to Courtney et al.). However, insome cases over time the positional error (i.e. the difference betweenthe desired or intended position of the motor's rotor and its actualposition relative to bodily tissue) can quickly grow to unacceptablelevels. Even small velocity errors in the motor, when accumulated, canmake an image appear to rotate on an ultrasound viewing screen orconsole, giving the impression that the imaging device is beingphysically rotated within the body even though it is stationary.

To address such a disconcerting or confusing and false effect, a rotaryfeedback mechanism may be used to precisely measure angular position sothat each image frame acquired through ultrasound imaging is registered(i.e. oriented appropriately) with respect to previous frames. While avariety of rotary encoders are commercially available, such as halleffect sensors, incremental quadrature encoders, absolute gray encodersand potentiometers, such off-the-shelf devices are too bulky and complexto fit into an intravascular or other low profile device. There is thusa need for a registering device or system that is reduced in bulk andsimpler, in order to maintain or reduce overall size and usability ofIVUS devices.

SUMMARY

Among other things, there is disclosed an internal ultrasound devicewith a rotary feedback system for registering successive images with oneanother. In particular embodiments, an ultrasound device (e.g. anintravascular ultrasound or IVUS device) with a rotary feedback systemincludes a transducer for emitting an ultrasound beam, the beam beingrotatable around a longitudinal axis, and wherein the transducer isadapted to emit the beam and to receive reflected ultrasound andtransform the reflected ultrasound into electronic signals, and anultrasound control and/or analytical (e.g. imaging) systemelectronically connected to the transducer for receiving the electronicsignals from the transducer and for creating images from the electronicsignals. A wall surrounding the transducer has an ultrasoundattentuation that is different between two or more sections of the wall.The wall sections thus attenuate (e.g. reflects, refracts and/orabsorbs) the beam to different degrees, resulting in electronic signalsdiffering in at least one characteristic (e.g. amplitude) that isdistinguishable by the control system. The system is adapted to monitorthe electronic signals for one or more distinguishable characteristicsin the electronic signals and to correlate them to an angular position,e.g. in a succession of images.

In particular embodiments, an internal ultrasound device with a feedbacksystem includes a transducer for emitting and/or receiving an ultrasoundbeam, the beam adapted to rotate around at least a portion of thedevice, wherein the transducer is adapted to send electronic signals,the electronic signals representing one or more qualities of ultrasoundenergy along a path of the beam. A wall surrounds the transducer, thewall having a first portion affecting the ultrasound beam in a firstfashion (e.g. attenuating the ultrasound beam to a first degree) and asecond portion affecting the ultrasound beam in a second fashion (e.g.attenuating the ultrasound beam to a second degree which may bedifferent from the first degree), so that the ultrasound beam as itrotates at least periodically travels along a path that intersects thefirst wall portion (e.g. is along a line that includes or a path betweenthe first portion and the transducer), and as it rotates the beam atleast periodically travels along a path that intersects the second wallportion (e.g. a line that includes or a path between the second portionand the transducer). An ultrasound control system is electronicallyconnected to the transducer for receiving and assessing the electronicsignals from the transducer. A first electronic signal sent by thetransducer representing one or more qualities of ultrasound along a paththat intersects the first wall portion (e.g. between the transducer andthe first portion) has at least one characteristic different from asecond electronic signal sent by the transducer representing one or morequalities of ultrasound along a path that intersects the second wallportion (e.g. between the transducer and the second portion). Theultrasound control system is adapted to detect the at least onecharacteristic and to register a plurality of the electronic signalswith each other by reference to the at least one characteristic.

Specific examples include those in which the first and second portionsof the wall are located so that the ultrasound beam must travel furtherbefore interacting with the first portion than the ultrasound beam musttravel before interacting with the second portion, so that the firstelectronic signal is delayed relative to the second electronic signal,and those in which the first portion of the wall reflects at least aportion of the ultrasound beam so that the first electronic signal hasan amplitude greater than the amplitude of the second electronic signal.The second portion of the wall can include a material with a relativelow acoustic impedance (e.g. low mismatch with a surrounding or adjacentenvironment), and the first portion of the wall includes a linear memberwith a relative high acoustic impedance (e.g. high mismatch with asurrounding or adjacent environment). In the example of use in anenvironment within a blood vessel or adjacent tissues, the secondportion of the wall can include a material with acoustic impedance closeto that of water, and the first portion of the wall (e.g. a linearmember) is of or includes a material with acoustic impedance markedlyhigher than water. Such a linear member may be an electronic conductor,e.g. one connected to the transducer. Conductors can include a coaxialcable and/or a strip of metallic material. A linear member may be placedsubstantially parallel to an axis of rotation of the ultrasound beam. Insome embodiments, the first portion of the wall includes a film ofmetallic material, and the second portion of the wall does not includethe film of metallic material, so that the ultrasound attenuation of thefirst portion of the wall is different from the ultrasound attenuationof the second portion of the wall. A particular example is one in whichthere are two of the first portions and two of the second portions, thesecond portions being positioned at diametrically opposed locations. Thetwo second portions may separate the two first portions into first andsecond electrically conductive parts, each of which is electricallyconnected to the transducer, so that the first electrically conductivepart conducts signals to and/or from the transducer and the secondelectrically conductive portion is a ground. Suitable metallic materialsinclude at least one of gold, platinum, rhodium, silver, copper andaluminum, and suitable thicknesses of the film or layer includeapproximately 1 nm to 20 μm.

Embodiments of internal ultrasound devices are also disclosed thatinclude a transducer for emitting and receiving an ultrasound beam, thebeam adapted to rotate around at least a portion of the device, whereinthe transducer is adapted to send electronic signals, the electronicsignals representing one or more qualities of ultrasound energy along apath of the beam, and a wall surrounding the transducer, the wall havingan inner surface generally facing the transducer and an outer surfacegenerally facing away from the transducer. The inner surface includes afirst film of metallic material forming a first conductor, the firstconductor being electronically connected to the transducer, and whereinthe outer surface includes a second film of metallic material forming asecond conductor, the second conductor being electronically connected tothe transducer and electronically insulated from the first conductor.Particular examples have at least a portion of each of the first filmand second film overlapping each other with the wall between them. Otherembodiments may have first and second films or coatings on the samesurface that do not overlap, as by sectioning the inner (or outer) wallor circumference and placing two coatings electrically insulated fromeach other on separated halves or other sections of the inner (or outer)circumference, thus having the coatings on the same surface butelectrically isolated from one another. The first film can extend aroundthe entirety of the inner surface's internal perimeter, and/or thesecond film can extend around the entirety of the outer surface'sexternal perimeter. Specific embodiments use the first conductor as asignal conductor and/or the second conductor as a ground. The walldefines a window through which the ultrasound beam passes, and at leastone of the first and second conductors may be at least partially withinthe window, and in such cases the portion of the at least one of thefirst and second conductors within the window permit ultrasound imagingthrough them.

A number of arrangements for turning the ultrasound beam with respect tothe wall may be used. For example, the transducer may be directly orindirectly connected to a motor so that the transducer is rotatable inat least a 360 degree arc to turn the beam. As another example, thedevice may include a mirror that turns in at least a 360 degree path toreflect the beam from the transducer and the reflected ultrasound to thetransducer.

As further discussed below, embodiments of encoders that can be used inan ultrasound transducer assembly (e.g. for use in intravascularultrasound or IVUS) are disclosed. The ultrasound attenuationcharacteristic(s) of the housing or a wall portion for a transducerassembly are varied between or among at least two portions. As theultrasound beam is rotated, the beam will pass through regions withdifferent or varying levels of acoustic attenuation. Signals (e.g. RFsignals) received from the transducer (as a result of an ultrasoundsignal) are monitored for changes in amplitude or other characteristicswhich reflects the acoustic attenuation difference(s) in the wall, andthese signals (and the images or data created or derived from them) arecorrelated as to angular position of the beam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an embodiment of an internalultrasound device as further disclosed herein.

FIG. 2 is a schematic representation of an embodiment of an internalultrasound device as further disclosed herein.

FIG. 3 is a schematic representation of an embodiment of an ultrasoundfield produced by the embodiment of FIG. 1, viewed on and along alongitudinal axis.

FIG. 4 is a schematic representation of an embodiment of an ultrasoundfield produced by the embodiment of FIG. 2, viewed on and along alongitudinal axis.

FIG. 5 is a schematic representation of an embodiment of an internalultrasound device as further disclosed herein.

FIG. 6 is a schematic representation of an embodiment of a portion of aninternal ultrasound device as further disclosed herein.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

For the purposes of promoting an understanding of the principles of thedisclosure, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theclaims is thereby intended, such alterations and further modificationsin the illustrated embodiments, and such further applications of theprinciples of the disclosure as illustrated therein being contemplatedas would normally occur to one skilled in the art to which thedisclosure relates.

Referring now generally to the drawings, there are shown embodiments ofa device 20 for providing ultrasound inside the body. Such devices maybe diagnostic or therapeutic (including interventional) in application,and include devices inserted percutaneously, subcutaneously orendoluminally into the patient. Among other things, this disclosureprovides an ultrasound encoder inside of an acoustic window (e.g. aportion of a catheter wall) without sacrificing image quality. Twotechniques are suggested, one of which focuses on reflection, by addingone or more markers to a catheter wall that strongly reflect ultrasound.The marker may be small so that the reflected ultrasound energy is smalland overall image quality is not affected. Another technique focuses onattenuation, by varying the attenuation or acoustic impedance ofdiscrete areas or portions of a catheter wall so that the amplitude ofan electrical (e.g. RF) signal produced by a transducer will bedependent on the angular position, i.e., the portion of the wall throughwhich an ultrasound beam and its echoes pass. The shape of areas withdifferent acoustic attenuation can be arbitrary, small or large, but inpreferred embodiments are larger than beam width. Examples of suchdevices include embodiments designed for intravascular ultrasound (IVUS)imaging or treatment of deep vein thrombosis (DVT).

In the embodiment shown schematically in FIG. 1, device 20 is a flexibleelongated member 22 (e.g. a catheter or other tubular member) having awall 24 defining an internal chamber 26, with catheter 22 being sizedand configured for insertion into and/or travel along the vascularsystem. Within chamber 26 is a transducer 28, which in this embodimentis for emitting an ultrasound beam and for receiving reflectedultrasound and sending electronic signals representing the reflectedultrasound. The illustrated embodiment includes an ultrasound reflectivemirror 30, which is mounted to a rotary motor 32. It will be understoodthat transducer 28 could be connected (directly or indirectly) to motor32 instead of mirror 30. An imaging system 34 is electronicallyconnected to transducer 28, for displaying ultrasound images. Otherfeatures may be included in device 22, such as a two-axis gimbal mountor other pivoting mechanism for transducer 28 or mirror 30, to provide awider or variable ultrasound field, and/or a linear motor with a shaftfor forcing the mount and/or the transducer 28 to pivot. Examples areshown in the application filed on Oct. 12, 2012, entitled “Devices andMethods for Three-Dimensional Internal Ultrasound Usage” (ApplicationSer. No. 61/713,172), which is incorporated herein in its entirety.

Catheter 22 in the illustrated embodiment is an elongated device ofplastic or other sturdy flexible material that presents a barrier to thepassage of ultrasound signals small enough (i.e. the difference inacoustic impedance at the boundary of the material and the substancesadjacent it) that ultrasound images may be reasonably acquired throughthe barrier. Wall 24 is a part of catheter 22 in this embodiment andthus is of the same ultrasound-transparent material. It surrounds atleast part of chamber 26, which is at the distal end of device 20 in theillustrated embodiment, and extends proximally. The proximal end of wall24 and/or catheter 22 may extend outside of the patient during use, andmay end in a handle or other operating portion, such as imaging system34 or a connection imaging system 34. Particular embodiments of catheter22 or at least chamber 26 are cylindrical, and are sized for insertioninto and passage through blood vessels, such as insertion into thefemoral artery and passage through it toward the heart. At least aportion of wall 24 defines an ultrasound field or window 36 throughwhich an ultrasound beam from transducer 28 exits, and through whichreflected ultrasound travels to return to transducer 28.

Wall 24 may have a port 27 or other feature to allow injection of fluidinto chamber 26. To address ultrasound reflectivity at the boundarybetween chamber 26 and blood or other body fluid in which device 20 isplaced, a fluid F is placed in chamber 26 that presentsultrasound-carrying characteristics that are similar to the fluidoutside of chamber 26. In particular embodiments, fluid F is a salinesolution, so that the ultrasound characteristics within chamber 26(saline) are similar to those outside chamber 26 (blood in a bloodvessel). Port 27 allows a user to inject fluid F into chamber 26 justprior to use of device 20. Port P can then self-seal, so that little orno fluid F escapes from chamber 26. One or more seals may be placed indevice 20 to separate fluid F in chamber 26 from motor 32.

Transducer 28 is indicated schematically in the drawings. The term“transducer” should be understood to include an assembly of two or moreparts as well as a single piece. It will further be understood that“transducer” as used herein includes devices that transmit ultrasound(i.e. transform an electrical (RF) signal to ultrasound), receiveultrasound (i.e. transform ultrasound to an electrical (RF) signal), orboth. If multiple transducers or pieces are provided, transmission ofultrasound may occur at one and reception at another. Transducer(s) asdescribed herein may have one or more piezoelectric elements asrespective transducers, and may operate in combination with othertransducers within or outside the body.

An exemplary transducer 28 includes a body or backing layer 40 with apiezoelectric element 42 attached to one side of body 40, and one ormore clamping rings 44. An impedance matching layer (not shown) may alsobe attached to transducer element 42, e.g. opposite body 40 Transducer28 is positioned at a far (i.e. further distant from the user) portionof chamber 26 and catheter 22 in the embodiments of FIGS. 1 and 2, withelement 42 facing longitudinally and proximally as indicated in thedrawings. Mirror 30 includes a surface 46 that reflects an ultrasoundbeam laterally (i.e. generally away from the longitudinal axis ofcatheter 22) through wall 24 within field 36. In the embodiment of FIG.5, transducer 28 is attached to motor 32 so as to provide a generallylateral ultrasound beam direction. Body 40 may be substantially opaqueto or reflective of ultrasound signals, so that such signals areeffectively only projected laterally outward from piezoelectric element42, e.g. to one side or in a limited angular range radially fromtransducer 28.

Rotary motor 32 includes a rotating shaft 70, for direct or indirectconnection to mirror 30 (e.g. FIGS. 1 and 2) or transducer 28 (e.g. FIG.5) in these embodiments. Rotary motor 32 is a microminiature motorsuitable for containment within chamber 26 of catheter 22, preferably ofa size of less than about 2.8 mm in diameter. Examples of suchmicrominiature motors include piezoelectric or electromagnetic motors.For example, a particular embodiment of motor 32 is a two-phase,coreless, brushless DC electromagnetic motor, which has few components,small size and minimal complexity. Shaft 70 is hollow in the embodimentof FIG. 1 (i.e. defining a lumen 72 therethrough) and extends throughthe entirety of motor 32 (e.g. a dual shaft motor). Lumen 72 throughshaft 70 permits passage of electronic conductors, (e.g. wires orcables), pulling or pushing mechanisms, and/or other features to passthrough shaft 70, allowing transmission of electrical and/or mechanicalforce or energy through lumen 72 without affecting the turning of shaft70.

Rotary motor 32 in the illustrated embodiments is configured to rotateshaft 70 continuously in a single rotational direction. In suchembodiments, the ultrasound beam emitted by transducer 28 is rotatedaround the longitudinal axis of shaft 70 in that single rotationaldirection. It will be understood that rotary motor 32 may alternativelybe configured to run in a reciprocating motion, with shaft 70 switchingbetween rotation in a first rotary direction (e.g. for a predeterminedtime or number of turns) and rotation in a second, opposite, rotarydirection (e.g. for a predetermined time or number of turns). An exampleof such a reciprocating device is described in Application Ser. No.61/713,135, entitled “Reciprocating Internal Ultrasound TransducerAssembly” filed on Oct. 12, 2012, which is incorporated by referenceherein in its entirety. As seen in the drawings, mirror 30 or transducer28 can be fixedly mounted to shaft 70, which is along the overalllongitudinal axis of device 20. As shaft or rotor 70 rotates, theultrasound beam emitted by transducer 28 rotates at the same speed.

In the illustrated embodiments, the ultrasound beam or signals emittedand received by transducer 28 are used as a feedback mechanism toprecisely assess or monitor the rotational position of rotary motor 32(and the ultrasound beam rotated by it) relative to the rest of device20, ensuring proper registration of images obtained through transducer28. The illustrated embodiments include at least one feature thatattenuates at least a portion of the ultrasound beam as it leavescatheter 22 at least one discrete location. For example, the embodimentshown in FIG. 1 includes a coaxial cable 80 fixed to the interior ofwall 24 (i.e. within chamber 26) and passing through the ultrasoundfield 36 (i.e. the area through which the ultrasound beam from element42 passes as the beam turns or sweeps during turning by motor 32). Cable80 in a particular example has a first channel or conductor 82 to powertransducer 28, and a second channel or conductor 84 to conduct signalsgenerated by reception of ultrasound signals by element 42 to imagingsystem 34. Cable 80 also serves as a linear marker that attenuates theultrasound beam (for example by reflection) to a greater degree thanwall 24 attenuates the ultrasound beam. The greater attenuation of cable80 amidst the much smaller attenuation (e.g. through reflection,refraction, scattering or absorption) of wall 24 presents a variedattenuation condition for wall 24, in which ultrasound (emitted beam orreflected echoes) relatively easily moves through or across wall 24except where cable 80 lies. Thus, an ultrasound signal produced at thediscrete location of cable 80 within window or field 36 is substantiallydifferent from those produced at other locations within field 36, whichresults in a substantially different RF signal produced by transducer 28for sending to a viewer. For example, the RF signal relating to thediscrete location of cable 80 may have a much larger amplitude,indicating substantial reflection from that location, than is otherwiseproduced by transducer 28 relative to other locations on wall 24. Asanother example, the RF signal relating to that discrete location mayhave a much smaller amplitude (or close to zero) than other signals,indicating blockage of ultrasound approaching transducer 28 by cable 80.In some embodiments, the reflection, blockage or other attenuation dueto cable 80 may extend to an angle B (see FIG. 3), which may be about 15degrees of arc in ultrasound field 36 ( 1/24 of the image area).

In the illustrated embodiment, cable 80 is parallel to the longitudinalaxis A of device 20 through the entirety of ultrasound field 36. As theultrasound beam proceeds around the circumference of wall 24, it will beattenuated substantially uniformly by wall 24—for instance, wall 24 willpass all or a substantially uniform fraction of the ultrasound energy inthe beam. When the ultrasound beam encounters cable 80, cable 80 blockssome or all of the beam directed at it. The reflected ultrasound at thatdiscrete location (e.g. region B in FIG. 3) will produce an RF signal(representing echo(es) received by transducer 28) markedly differentfrom the regions of the ultrasound field without cable 80. For example,the RF signal produced from emissions directed toward or received fromthe direction of cable 80 may be substantially more powerful (e.g. agreater intensity) than that received at other locations along wall 24,indicative of essentially entire reflection of the ultrasound beam bycable 80. As another example, the RF signal may be or approach zerobecause cable 80 scatters the ultrasound beam, and no return ultrasoundecho can approach transducer 28 through cable 80. When the distinctivesignal is encountered by imaging system 34 (e.g. viewing software andapparatus), imaging system 34 observes that distinctive signal anddetermines that the beam is pointed toward cable 80. Accordingly, theposition of the ultrasound beam with respect to cable 80 on wall 24,other static portions of device 20, and/or tissue or marker within thebody is known with precision. Image frames (e.g. successive frames) areregistered by imaging system 34 using the distinctive signalcharacteristic provided by cable 80 as a marker or indicator of thestatic position of cable 80, so that successive images are displayed inthe same position and/or orientation for viewing by the physician orother operator.

Cable 80 is shown in this embodiment to be inside chamber 26, on aninterior surface of wall 24. It will be understood that cable 80 couldbe arranged on the outside of device 20 along wall 24, but anarrangement in which cable 80 is within chamber 26 does not increase theoutside diameter of device 20 or provide it with an irregular outersurface, which may be disadvantageous in the realm of intravascularusage. In other embodiments, cable 80 is placed within wall 24, i.e.between its inner and outer diameters among the matter of wall 24. Forexample, cable 80 may be placed in forming wall 24 initially, or betweenlayers of material in wall 24. Such an arrangement does not enlarge orpresent an odd outer configuration, and maintains a maximum of spacewithin chamber 26 for the operating components. Further, if cable 80 isnot needed for transfer of electrical signals to or from transducer 28,a metallic strip or layer may be placed in wall 24 or on a surfacethereof to provide the attenuation noted above. Such a strip or layerprovides an even lower profile for the device.

It will be appreciated that a variety of materials or features thatcreate the varied-attenuation wall 24, as by partially or fully blockingultrasound to an extent different than any blockage provided by the restof wall 24, can be used as an encoder or registration tool. For example,in the embodiment shown in FIG. 2, two sections 90, 92 of a thin metalfilm, coating or layer are placed on wall 24. The particular embodimentshown has sections 90, 92 on the interior of wall 24 (i.e. facing oradjoining chamber 26), although it will be understood that such sections90, 92 may be placed on the outside of wall 24 or within wall 24, i.e.between its inner and outer diameters. In the embodiment of FIG. 3, thefilm is deposited on the inside of wall 24 using techniques such assputtering or electro-plating, and in other embodiments may be placedoutside (on the outer surface of) wall 24. In particular embodiments,only one side of the ultrasound window (e.g. the inside or the outside)is coated with the thin film to minimize acoustic attenuation. Theillustrated embodiment shows two sections 90, 92 separated by two openor uncovered portions 94, 96. Portions 94, 96 are diametrically opposedto each other and subtend substantially the same arc in this embodiment.It will be understood that a single open portion or more than two suchopen portions may be provided.

It will be understood that a number of substances providing a differencein ultrasound attenuation may be used for a film or layer in sections90, 92. Metals (e.g. aluminum) have been used for electricalconductivity, and particular embodiments of a thin conductive layer forsections 90, 92 of gold, platinum, or rhodium may be used for theirbiocompatibility, high conductivity and resistance to oxidation. Usingefficient conductors of electricity for the film in sections 90, 92permits use of those sections 90, 92 to conduct electrical signalsthrough the ultrasound field as well as providing a difference inultrasound attenuation in field 36 in the varied-attenuation wall 24 ofdevice 20. Such a thin conductive film has high electrical conductivityas well as allowing acoustic transmission, allowing an ultrasound windowhaving such a film to conduct signals across or through the window (i.e.along the longitudinal axis) while obtaining a viewable image behind theconductor. In particular embodiments, the layers or coatings are betweenabout 0.1 μm and 20 μm in thickness, such as approximately 2 μm thick.The sections cover more than half of the ultrasound window in certainembodiments, and a particular example (e.g. FIG. 4) each section 90, 92covers about 150 degrees of the window, with uncoated areas between themeach covering about 30 degrees and diametrically opposed to each other.In other embodiments, the respective arcs subtended by sections 90, 92may be up to about 160, up to about 170 or up to about 175 degrees. Itwill also be understood that in other embodiments the arcuate extent ofsections 90, 92 (and/or the spaces between them) may be unequal.

Such thicknesses have been tested and found to operate as desired.Thicker layers may be usable, but will increase acoustic reflection (andtherefore a reduction in the acoustic energy passed through wall 24 inboth exit and return) and reduce loss of electrical signal, andvice-versa. Both such losses degrade image quality and shouldaccordingly be minimized. Acoustic reflectivity (and therefore acousticloss in the device 20) is related to the impedance mismatch between thefilm and the surrounding materials (e.g. water or blood), filmthickness, and ultrasonic wave frequency. From testing, it has beenfound that a 16 μm thick aluminum film results in an acoustic loss ofless than 4 dB in a round trip, i.e. a pulse echo from transducer 28outward and back, twice through the film(s) on ultrasound window. It isexpected that a thin gold film will cause less than 5 dB of ultrasoundattenuation during such a round trip.

Embodiments using a thin metallic layer or coating as noted aboveprovide the advantage of imaging in a complete 360 degree area, whilestill permitting registration of images. As seen schematically in FIGS.3-4, embodiments using a cable or other elongated sideultrasound-reflective (e.g. having a high acoustic impedance) piece arecompared to those using a thin film as acoustic attenuator. In FIG. 3,the ultrasound beam turns around an axis perpendicular to (out of) thepage, with cable 80 statically placed to one side on wall 24. Outercircle 100 represents an area (e.g. tissue such as a blood vessel) to beimaged, showing an interior in which the ultrasound beam travels. As thebeam turns, each revolution passes cable 80, which generates anunvisualizable or less-visualizable wedge area 102 behind cable 80. Asindicated above, that area 102 may be an area of about 15 degrees of arcor less. The remainder of the tissue or area is easily imaged, and thewedge area 102 remains static and is used to register images with oneanother, as discussed above.

In FIG. 4, the beam likewise turns around an axis out of the page, andhas two sections 90, 92 of thin metallic layer along wall 24. The layer,as discussed previously, allows acoustic transmission but to a lesserdegree than the open spaces 94, 96 between sections 90, 92. Again, outercircle 100 in FIG. 4 represents area (e.g. a vessel portion) to beimaged. As the beam turns, it passes through sections 90, 92 with someattenuation, but with sufficient acoustic energy moving through sections90, 92 to image the desired area. Open spaces 94, 96 provide a strongeracoustic signal return to transducer 28, which is used for registrationof images. The coated or layered sections 90, 92 reduce the imagequality slightly and limits the total imaging depth over a larger arc,but allow imaging over the whole ultrasound field or window 36, whilethe cable 80 prevents or limits visualization in an angle behind it butdoes not affect visualization in other parts of the field or window 36.

In the example in which two sections 90, 92 are coated with the thinlayer, with an uncoated area separating the sections, the sections canhave separate electrical functions. For example, one section 90 cancarry electronic (RF) signals to and from transducer 28, to powertransducer 28 to emit an ultrasound beam and to carry the signal fromtransducer 28 representing the reflection of the ultrasound beam, forgenerating the image of the tissue. The other section 92 can function asa ground. Thus, the uncoated areas 94, 96 function both for registrationof the images, since they allow through a different strength of signalfrom that allowed through sections 90, 92, and for the electricalinsulation of the sections 90, 92 from each other.

It will also be understood that thin films or layers of metallic orother conductive materials may be used as conductors for transducer 28or for other uses in other ways. Referring generally to FIG. 5, there isshown an embodiment of an internal ultrasound device 120 having aflexible elongated member 22 (e.g. a catheter or other tubular member)with a wall 24 defining an internal chamber 26, with catheter 22 beingsized and configured for insertion into and/or travel along the vascularsystem. Within chamber 26 is a transducer 28, which in this embodimentis for emitting an ultrasound beam and for receiving reflectedultrasound and sending electronic signals representing the reflectedultrasound. A window or field 36 for the ultrasound beam is indicated.Member 22, wall 24, chamber 26, transducer 28 and window 36 are allsimilar or identical to embodiments described above.

Wall 24 includes an inner surface 131 generally facing transducer 28(e.g. inward toward the longitudinal axis of device 120) and an outersurface 133 generally facing away from transducer 28. Inner surface 131will thus generally define at least a portion of chamber 26. On at leasta portion of inner surface 131, there is a film or thin layer 190 ofmetallic material, as for example one or more of the materials notedabove with respect to sections 90, 92. In the illustrated embodiment,film 190 extends all the way around the perimeter (in this case, acircumference) of inner surface 131, and is within a part of window 36.In other embodiments, film 190 may extend less than all the way aroundthe perimeter. Further, other embodiments may include a film 190 havinga length along the longitudinal axis of device 120 that encompasses allof window 36, or that is not within window 36 at all. Similarly, atleast a portion of outer surface 133 includes a film or thin layer 192of metallic material. In the illustrated embodiment, film 192 extendsall the way around the perimeter (in this case, a circumference) ofouter surface 133, and is within a part of window 36. In otherembodiments, film 192 may extend less than all the way around theperimeter. Further, other embodiments may include a film 192 having alength along the longitudinal axis of device 120 that encompasses all ofwindow 36, or that is not within window 36 at all. The illustratedembodiment shows films 190, 192 overlapping each other, i.e. a diameterof device 20 intersects each film 190, 192, while they are separated bywall 24. It will be understood that other embodiments may have first andsecond films or coatings (e.g. films 190, 192) on the same surface (e.g.one of surfaces 131 and 133) that do not overlap. For example, twocoatings 190, 192 can be placed, electrically insulated from each other(e.g. by a non-conductive space), on separate halves, opposed areas, onthe same side of window 36 (e.g. each or both covering a part of theperimeter of window 36), or other sections of the inner surface 131 orof the outer surface 133, thus having the coatings on the same surfacebut electrically isolated from one another.

Another embodiment of placement of films 190, 192 is shown schematicallyin FIG. 6, in which film 190 is on an inner surface 131 in one area ofwindow 36, and film 192 is on an outer surface 133 in another area ofwindow 36. The illustration shows that films 190 and 192 extend aboutseparate arcs of about 180 degrees, so that they do not overlap. It willbe understood that films 190, 192 may each cover a smaller arc, may eachcover different arcs from each other, and may be opposite each other orotherwise placed. Such an embodiment provides an effect on an ultrasoundbeam that is different in the area covered by film 190 compared to thatcovered by film 192, at least because of the differing travel distancefor the ultrasound beam to move from a transducer or reflector to therespective films 190, 192. Thus, the ultrasound beam that travels alonga path intersecting film 192 travels a longer distance (and takes alonger time) before encountering film 192 compared to the distance andtime for the ultrasound beam that travels along a path intersecting film190. Other effects on the ultrasound beam by films 190, 192 or otherpieces (as noted herein) may also be present.

Films 190, 192 form separate electronic conductors that are insulatedfrom each other, as by the material of wall 24 in the illustratedembodiment. Each of films 190, 192 are separately electronicallyconnected to transducer 28 in this embodiment, so that one film acts asa signal conductor and the other as a ground. In the example of FIG. 5,the outer film 192 is the ground, and inner film 190 is the signalconductor. Films 190, 192 may be of the same materials and prepared insubstantially the same or identical ways as sections 90, 92 noted above.When of a thickness as noted above, films 190, 192 permit ultrasoundimaging through them, even though there may be attenuation (as byreflection, refraction or absorption). It will be understood that films190, 192 as conductors may be used with or without the feedback orregistration characteristics discussed above with respect to sections90, 92. For example, in embodiments in which both films 190, 192 extendaround their respective perimeters and extend along most or all ofwindow 36, the attenuation due to films 190, 192 will be substantiallyconstant within window 36, so that electronic signals sent by thetransducer will not have an amplitude or other difference that permitregistration or alignment of signals or images.

While the embodiments have been illustrated and described in detail inthe drawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly particular embodiments have been shown and described and that allchanges and modifications that come within the spirit of the disclosureare desired to be protected. Examples of other features or embodimentsuseful in connection with the particular embodiments discussed above arefound in the application filed on Oct. 12, 2012, entitled “MechanicalScanning Ultrasound Transducer with Micromotor” (Application Ser. No.61/713,186), which is incorporated herein in its entirety. It will beunderstood that features or attributes noted with respect to one or morespecific embodiments may be used or incorporated into other embodimentsof the structures and methods disclosed.

What is claimed is:
 1. An internal ultrasound device with a feedbacksystem, comprising: a transducer for emitting and/or receiving anultrasound beam, the beam adapted to rotate around at least a portion ofthe device; an ultrasound-transparent wall through which at least partof the ultrasound beam passes, the wall having an external diameter, thewall having two first portions of the wall separated by a second portionof the wall, each first portion of the wall with a thin metal filmentirely inside the external diameter, the thin metal films havingelectrical conductivity and allowing passage of an ultrasound beam,wherein the thin metal film of a first of the two first portions of thewall is electrically connected to the transducer to carry signals to andfrom the transducer, and the thin metal film of a second of the twofirst portions is grounded, and wherein the ultrasound beam, as itrotates, at least periodically travels along a first path thatintersects any of the two first portions of the wall and the transducerso that the ultrasound beam passes through the thin metal film with someattenuation and a second path that intersects the second portion of thewall and the transducer, so that a first electronic signal generated bythe transducer representing received ultrasound along the first path hasat least one signal characteristic different from a second electronicsignal generated by the transducer representing received ultrasoundalong the second path; and an ultrasound control system adapted to:receive and assess a plurality of electronic signals from the transducerrepresenting received ultrasound along a path of the ultrasound beam asthe ultrasound beam rotates, detect the at least one signalcharacteristic difference amongst the plurality of electronic signals,and register the plurality of the electronic signals with each other byreference to the detected at least one signal characteristic difference.2. The device of claim 1, wherein the first portion of the wall isconfigured to attenuate the ultrasound beam to a first degree and thesecond portion of the wall is configured to attenuate the ultrasoundbeam to a second degree.
 3. The device of claim 1, wherein the secondportion of the wall does not include a thin metal film, so that theultrasound attenuation due to interaction with the first portions of thewall is different from ultrasound attenuation due to interaction withthe second portion of the wall.
 4. The device of claim 1, comprising twoof the second portions, the second portions being positioned atdiametrically opposed locations.
 5. The device of claim 1, wherein thethin metal film comprises at least one of gold, platinum, rhodium,silver, copper and aluminum.
 6. The device of claim 1, wherein thethickness of the thin metal film is approximately 1 μm to 20 μm.
 7. Thedevice of claim 1, wherein the transducer is configured to: emit theultrasound beam, and rotate in at least a 360 degree arc to turn thebeam.
 8. The device of claim 1, wherein the transducer is configured toemit and receive the ultrasound beam, the device further comprising amirror configured to turn in at least a 360 degree path to reflect theemitted ultrasound beam from the transducer and reflect the receivedultrasound beam to the transducer.
 9. The device of claim 1, wherein thetwo first portions of the wall each subtend an arc along the wall, thearc's central angle within the range of 150 degrees to 175 degrees. 10.The device of claim 1, wherein the wall has an inner surface facing thetransducer and defining an inner diameter, and the thin metal film isdisposed on the inner surface.
 11. The device of claim 1, wherein thewall has an inner surface facing the transducer and defining an innerdiameter, and wherein the thin metal film is disposed in the wall,between the inner diameter and the outer diameter.
 12. The device ofclaim 1, wherein an ultrasound beam from the transducer that passesoutward through the thin metal film and returns as an echo through thethin metal film to the transducer experiences an acoustic loss, due tointeraction with the thin metal film, of less than 5 dB and greater than0 dB.
 13. An internal ultrasound device with a feedback systemcomprising: a transducer for emitting and/or receiving an ultrasoundbeam, the beam adapted to rotate around at least a portion of thedevice; an ultrasound-transparent wall through which at least part ofthe ultrasound beam passes, the wall having an external diameter, thewall having a first portion of the wall with a first thin metal filmdisposed thereon and a second portion of the wall with a second thinmetal film disposed thereon, the thin metal films having electricalconductivity and allowing passage of an ultrasound beam, wherein thefirst thin metal film is electrically connected to the transducer tocarry signals to and from the transducer, and the second thin metal filmis grounded, wherein the ultrasound beam, as it rotates, at leastperiodically travels along a first path that intersects the firstportion of the wall and the transducer so that the ultrasound beampasses through the first thin metal film with some interactiontherebetween and a second path that intersects the second portion of thewall and the transducer so that the ultrasound beam passes through thesecond thin metal film with some interaction therebetween, and whereinthe first and second thin metal films are located so that the ultrasoundbeam must travel further before interacting with the first thin metalfilm than the ultrasound beam must travel before interacting with thesecond thin metal film, so that at least one first signal characteristicof a first electronic signal generated by the transducer representinginteraction between the first thin metal film and received ultrasoundalong the first path is delayed relative to at least one second signalcharacteristic of a second electronic signal generated by the transducerrepresenting interaction between the second thin metal film and receivedultrasound along the second path; and an ultrasound control systemadapted to: receive and assess a plurality of electronic signals fromthe transducer representing received ultrasound along a path of theultrasound beam as the ultrasound beam rotates, detect, from amongst theplurality of electronic signals, the at least one first characteristic,the at least one second characteristic, and the relative delaytherebetween, and register the plurality of the electronic signals witheach other by reference to the detected delay.